The consumer demand for sweet-tasting products appears ever-increasing. However, the traditional naturally-derived sweeteners, particularly sucrose, suffer from the major drawbacks that they are high in energy content (“high in Calories”), leading to a risk of obesity and associated health problems. They are also associated with tooth decay.
There has hence been an enormous amount of work on developing synthetic sweeteners, which have little or no cariogenic effect, and which are far sweeter than sucrose, gram for gram, so that they may be used at lower levels, contributing fewer so-called “empty Calories” to the consumers' dietary intake. However, many of the products developed have proven to have undesirable properties, such as aftertaste, mouth feel or dietary intolerances amongst a substantial proportion of consumers. Additionally, to be as sure as possible that an artificial sweetener is safe (particularly in long-term use) requires lengthy and expensive testing.
There is hence also significant interest in alternative naturally-occurring sweeteners. Thaumatin is a particularly interesting example, with many advantages.
Thaumatin comprises a group of very closely related naturally-occurring proteins, each having a single polypeptide chain of 207 amino acid residues linked by 8 disulphide bridges, giving a molecular weight of around 22,000. There are no unusual or rarely-occurring amino acids in the chain, which means that hydrolysis (e.g. on digestion) is most unlikely to produce any substances associated with dietary intolerances.
Thaumatin is obtained from the West African plant Thaumatococcus daniellii. The Katemfe fruit from this plant has long been known as a source of sweetness, but was only reported in European scientific literature in 1855. It is now extracted on a commercial basis from Katemfe fruit, yielding a product that is roughly 2000 to 3000 times sweeter than sucrose (on a weight for weight basis). The effective “Calorie content” for a given sweetness level is hence close to zero. In line with the natural origin and long history of use of thaumatin, it is very widely approved for use as a sweetener and food additive. For example, the Food and Drug Administration (FDA) in the USA classifies thaumatin as GRAS (Generally Regarded As Safe). Thaumatin was approved in 1988 by the predecessor of EFSA (European Food Safety Agency) and in 1985 by the Joint FAO/WHO Expert Committee on Food Additives. Under the relevant European Directives, thaumatin may be used as a sweetener at certain maximum levels, depending on the food category involved, while when used as a flavour enhancer it can be used in any food made under GMP (Good Manufacturing Practice). Thaumatin has passed every animal and human safety study carried out to date, with no adverse reactions observed.
Thaumatin is also stable in freeze-dried form and in solution in water or aqueous alcohol. It survives pasteurisation and UHT processing conditions, and as a coating has survived dry temperatures up to 140° C. In aqueous solution, it is stable over a wide pH range. Thaumatin appears to have no cariogenic effects.
Thaumatin is not a complete replacement for sucrose, however. While it produces an intense sweetness, this is recognisably different to that of sucrose. The onset of the sweet taste is often delayed, while the perception of sweetness can then linger for longer than for sucrose. At high usage levels, a liquorice-like aftertaste can remain.
Nevertheless, thaumatin has several further properties that distinguish it from other natural and artificial sweeteners.
It has been found to act synergistically with other low-calorie sweeteners, producing significantly higher perceived sweetness than would be expected from the levels of thaumatin and the other sweetener present.
Additionally, thaumatin has been found to be more effective in masking many bitter, sour or metallic tastes than would be expected from its sweetness alone. This is beneficial both in foods (the metallic aftertaste of saccharine can be masked in addition to synergetically enhancing sweetness) and in pharmaceuticals (where many active components delivered by mouth have unpleasant tastes).
Thirdly, thaumatin enhances a wide range of non-sweetener flavour compounds, including savoury flavours, and in particular those considered “aggressive”. One example is the boosting of coffee flavour without generating bitter notes. In savoury products, there appears to be a more complex enhancement, involving synergies with natural flavour enhancers, such as 5′ nucleotides and monosodium glutamate (MSG). Thus, the taste element known from Japanese as “umami” can be enhanced without engaging the health risks perceived in some quarters from high MSG contents.
Thaumatin may thus be considered as much a flavour enhancer as it is a simple sweetener. However, it would still be beneficial if thaumatin could be “tailored” to produce any one of the above effects more than the others, it being rare to require all of the above properties at once. One might also for example wish to enhance a savoury taste without introducing noticeable sweetness, or enhance sweetness without masking a sour or bitter note. On the other hand, it is both a real and a perceived advantage of thaumatin that it is a natural plant extract, so chemical modification of the protein chain, for example, is unlikely to be an acceptable approach.
The process for extracting thaumatin essentially proceeds as follows (a more complete description is given in the examples below).
The flesh of the Katemfe fruit is excised from the seeds and is frozen for transport and storage. This flesh is “mashed” in an aqueous extraction step, filtered and treated with caustic soda. After sedimentation, the supernatant is decanted off, filtered and then concentrated and purified by membrane techniques. The concentrate is then induced to crystallise by reducing the temperature to well below 0° C. The crystals are vacuum-dried, granulated by ball-milling, sieved and blended with materials such as maltodextrin, gum arabic, lactose and the like to produce a convenient dry powder product containing a standard level of thaumatin protein.
It would be beneficial if variations in said conventional production process could be used to modify selectively the balance of properties of the thaumatin compositions produced.
It is hence an object of the present invention to provide a process for the production of thaumatin compositions that provides some or all of the above benefits and obviates some or all of the above problems. It is also an object of the present invention to provide thaumatin compositions having said modified properties.